Current Trill specification (RFC 6325—“Routing Bridges (RBridges): Base Protocol Specification”, hereby incorporated by reference in its entirety) requires Trill compliant RBridges to send multiple hellos on each interface, on a subset of enabled vlans. Specifically, depending on the appointed forwarder and the role or lack thereof of the designated RBridge, nodes must send out hellos on the following vlans, where announcing vlans are a subset of the enabled vlans on the network
If the sender is a designated RBridge, hellos must be sent to the intersection set of 1) the enabled vlans and 2) the union of (designated vlan, announcing vlans). If the sender is not a designated RBridge, hellos must be sent to the intersection set of 1) the enabled vlans and 2) the union of (designated vlan, intersection of (forwarding vlans, announcing vlans).
Based on these current stipulations, in the case where a LAN has several thousand vlans in active use, at a minimum the appointed forwarders will need to send out hellos on all of the vlans for which they are the appointed forwarder. This leads to a situation where the CPU (control plane) needs to send out thousands of hellos per interface on several hundred interfaces. This situation leads immediately to a scale problem. There exists a need for the optimization of Trill LAN Hellos.